Hydraulic system



l LL MERCURY 8 M/NOR PORT/ON 0F HYDRAULIC UER/EATING FLU/D HYDRAULIC LUBR/CAT/NG FLU/D INVENTOR WERN ER W. HOHENN ER ATTORNEYS United States Patent O HYDRAULIC SYSTEMy Werner WL Hohenner, Camarillo, Calif;

Application January 7,1954, Serial. No. 402,833

7j Claims. (Cl. 60-53) (Granted under Title 35, U. S. Code (1952), sec. 266) The inventionA described' herein may be manufactured and used by or forthe Government of the United States of America forl governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to a hydraulic system for operation of a hydraulic motor, and is particularly concerned with a novel hydraulic system wherein a control valve actuated by electrical or radio signals is adapted to control llowA of a special hydraulic lluid to a hydraulic motor so as to provide a minimum lag or delay in response of the motor to actuation of said valve.

In the testing of guided missiles, a device known as a llight table is employed for simulatingl missile ilight conditions. A hydraulically operated motor is often used to actuate the flight table, that is, to impart motions thereto simulating or corresponding to the motions of a missile in flight. In they hydraulic system for controlling the motor, electrical or radio signalscorrespondingl to' certainy llight data are fed to a control valve which in turn: controls' the movement of hydraulic fluid to the motor inresponse tosuch signals. This hydraulic movement is converted in the motor to mechanical movement which is then impartedV to the flight table.

In equipment of the abovetype-presently in use, conventional hydraulic lluids are employed: However, as a. result of thev comparatively low naturali frequency of the column of lluid between the control valve and hydraulic motor,- the lag: in. response of the motor and flight. table to sudden changes in position of the control valve producedl by varying signalsv is a serious. obstacle to obtaining good results with this test equipment. The natural frequency of. ak hydraulic fluid is directly related to its degree of incompressibility. The latter may be expressed in terms of a compression factor which is the fractional amount of shrinkagel of a unit volume of iluid at a specific pressure.` The smaller the compression factor the greater is the degree of incompressibility and the4 higher the natural frequency and response of a particular hydraulicl fluid.

Thus, the compression. factor ofthe usual hydraulic fluids is about. 1/70 ofi their volumey ata pressure of 1000 p'. s; i. Byf replacing the present hydraulic fluids with their comparatively-low resistance to; compression and correspondingly large compression factor, by a lluidz of relatively high resistance to compression and small compression factor, e; g. mercury with a compression factor of about 1mg@ of` its'volume at 1000 p. s. i., the natural frequency and response of a volume of the hydraulic fluid is increased. However, the replacement of theusual hydraulic iluids by mercury is not practically feasible because of thedifficulties encountered in maintaining proper lubrication within theA system wherein mechanical parts of extremely close tolerances move at relatively'high speeds, and` alsoy because of they high cost of the large quantities of mercury required and itsl great weight.

Accordingly, oneA object of this inventionis to'4 provide anovel hydraulic system.- including; a hydraulic. motor having improved response characteristics in relation to control thereof by a hydraulic valve.

Another object is the provision of a novel hydraulic lluid system for operation of a hydraulic motor by means of a control valve so as to provide a minimum lag or delay in response of the motor to actuation of the valve.

Yet another object. is to afford a novel hydraulic lluid system employing a hydraulic fluid mass having a high natural frequency and high resistance to compression, and which also possesses lubricatingl properties.

A still further aim of the invention is to provide a hydraulic fluid system for circulation between a control valve adapted to be operatedv by radio or electrical signals, and a hydraulic motor, the. hydraulic fluid being especially designed to have. a low compression factor and high natural frequency while at the same time having mechanical lubrieatingl properties, so as. to afford substantially instantaneous response of the motor to actuation of thecontrol valve by saidsignals. i

vYet another object is the provision of a hydraulic system for control of a` hydraulic motor by a control valve wherein a novel combination of hydraulic iluids ilows under pressure fromv the control valve to the motor and back to the valve and such fluids are recirculated in another portion of the system to. afford an overall system which is elilcient, dependableversatile and comparatively inexpensive.

Other objects. and. many of the attendant advantages of this invention will be readily appreciated asv the same becomes better understood by referenceA to the following detailed description when; considered in. connection with the accompanying drawing. showing in schematic form a hydraulic system according to the invention.y

lt has been discovered that by combining a relatively small amount. of mercury together with the usual hydraulic fluids in a hydraulic. system. and by incorporating proper means, to enforce circulation of. such mixture predominating in mercury between the controlvalve and hydraulic motor of the. system, and advantages of'thecmercury', chiefly its small compression factor, and the advantages' of conventional hydraulic fluids, principally their, lubrication properties, are attained without. any ofthe disadvantages of the mercury or hydraulic lluids if used separately. Further, because the iniluence of the undesirably high compression factor of conventional hydraulic uid is essentially eliminated according to the invention, this carrier fluid can be chosen particularly for its lubricating or other pertinent properties, e. g. its heat dissipating properties.

Fluids having a low compression factor other than mercury may also be employed along with the usual hydraulic lluids having lubricating properties so long as the iluid of low compression factor is imiscible with the other lubricating fluids in the mixture. Further, mixtures of one or more` fluids of high resistance to compression such as. mercury can. be incorporated in a mixture of one or more conventional hydraulic fluids to produce the novely iluid system4 of the invention. v Mercury is the preferred. fluid of low compression factor or highv resistance to compression for the purposes of the invention.

Referring now to the drawing representing one embodiment of the invention, numeral l0 represents a control valve for regulating the llow of hydraulic fluid to a motor 12. Connecting an exit port 14 of the control valve with an intake port 1'6 of the motor is a'conduit 18, and a second conduit 20 connects an exit port 22 of the motor with an intake port 24 of the control valve. The control valve is of a type which is adapted to reverse the llow of iluid from` the valve to thel motor through conduits 18 and 20y so as to reverse the direction of rotation of the motor anda llight' table (not shown) coupled thereto. Any suitable conventional control valve, e. g.

a rotary type valve may be employed, and the motor is also of conventional design. The valve is adapted to be actuated by radio signals corresponding to missile flight data.

ln order to obtain maximum response of the motor and associated flight table to actuation of the control valve, a hydraulic mixture of high natural frequency according to the invention is circulated under pressure in conduits 1S and 20 between control valve l0 and the motor. ln the preferred embodiment this mixture consists of mercury and a conventional hydraulic fluid, c. g. of a kerosene base type. The mixture preferably predominates highly in mercury, and only a minor proportion of the conventional hydraulic fluid ingredient is present on a volumetric basis. For example, the mixture may contain from as little as .01% or less to volumetrically of the latter ingredient.

It has been found that best operation occurs with the use of the smallest amount of the hydraulic fluid ingredient possible to obtain proper lubrication of the control valve and motor. This enables use of a maximum proportion of mercury in the mixture, thus lowering the compression factor of the mixture until it closely appreaches that of pure mercury, the ideal situation. ln practice, the small amount of organic hydraulic fluid ingredient preferably employed in the mixture tends to flow along the inner walls of conduits 18 and 20 outside the main body of mercury therein, and when the mixture passes through the motor and valve, this small quantity of organic fluid ingredient sutlces to lubricate the moving parts of these members. However, the relative amount of lubricating fluid to mercury or other fluid of low compression factor in the mixture circulating between the control valve and motor may be varied in a manner described hereinafter to obtain a hydraulic mixture having the particular compression factor and lubricating properties desired.

After the hydraulic mixture has delivered its energy to the hydraulic motor and returned to control valve 10,

it is necessary to again pump the mixture up to the required pressure for repeating the cycle. However, particularly in the preferred case wherein such mixture contains a major proportion of mercury and only a very minor amount of organic lubricating fluid, it is necessary also to dissipate the large amount of heat generated in the hydraulic mixture after it has passed through the motor and is returned at a greatly reduced pressure to the control valve. Under these conditions, if the hydraulic mixture were simply pumped up to the required pressure again and recycled with no special provision made for dissipating the heat generated in the previous cycle, the mercury in the mixture would quickly evaporate. Hence, in addition to the provision of means for varying the ratio of hydraulic lubricating fluid to mercury in such mixture, means is also provided according to the invention for efficiently maintaining circulation of the desired mixture containing the preferred large amount of mercury, between the control valve and hydraulic motor without the necessity and expense of adding mercury to the overall system due to evaporation.

Accordingly, the invention device includes a sump 26, a separator 28 and a pump 30 for pumping fluid from the sump into the separator. Hot hydraulic mixture at a reduced pressure leaves the outlet port 32 of the control valve and is conveyed through pipes 34 and 36 to the sump. The latter contains a body of fluid consisting of a comparatively small amount of mercury 38 at the bottom of the vessel and a considerably larger proportion on a volumetric basis of lighter organic hydraulic fluid 40 floating on top of the mercury, such fluid being the same as that contained in the hydraulic mixture circulating between the control valve and hydraulic motor. The latter mixture flowing downwardly through pipe 36 drops from the lower end thereof into the top of the body of fluid at normal temperature in sump 26, and as the mercury in such mixture passes downwardly through the body of hydraulic fluid 40 to the pool of mercury at the bottom of the vessel, it is cooled by contact with the much cooler body of such fluid.

A pipe 42 extends downwardly through the organic fluid til in the sump, the lower extremity of such pipe communicating with the pool of mercury 38 at the bottom of the vessel and the upper extremity with the intake of the pump. Connected to the pump outlet is a pipe fr which communicates at its other end with thc top portion of separator 28. A return pipe 46 having a reduction valve 4S therein connects separator 28 at a point therein below the inlet of pipe 44, with pipe 36, and the lower portion of separator 28 communicates with an intake port 5G of the control valve by means of a pipe 52.

Mercury from pool 38 at thc bottom of sump 26 is pumped by means of pump 30 at high pressure into a body of organic hydraulic fluid 54 in separator 28, such fluid floating on a pool of mercury 56 in the bottom of the separator. The organic fluid 54 is of the same composition as the organic fluid 40 in sump 26, and as in the case of sump 26 the amount of such fluid present in thc separator is substantially greater on a volumetric basis than the amount of mercury in the separator. An injection Valve 58 is provided in conjunction with that portion of pipe 42 'within the fluid 40 in sump 26, for introduction of any desired amount of fluid 46 into pipe 42 and separator 2S along with mercury from pool 33, and an injection device including valve 6i) and tube 62 extending into pipe 52 is provided in separator 28 for introducing desired amounts of fluid 54 into the mercury 56 passing to the control valve.

That portion of the system between pump 30, valve if and motor 12, and including separator 2S, is under high pressure while the remainder of the system is at a much lower pressure. Thus, for example, the pressure in the high pressure portion of the system may range from 1,000 to 5,000 p. s. i.

Where that portion of the system between control valve 1i) and motor 12 is operating according to thc preferred embodiment of the invention with a maximum proportion of mercury and a minimum of hydraulic lubricating fluid in order to obtain a fluid mass of highest natural frequency in this portion of the system, the required small amount of lubricating fluid may be introduced into the mercury 56 passing to the control valve without actually opening valve 60. This is accomplished because` sufflcient lubricating fluid for this purpose tends to creep down from the fluid body 54 along the inner surface of the lower walls 64 of the separator beneath the mercury 56 therein, and continues to pass along the inner surface of pipe 52 into the control valve along with the mercury. Under these conditions injection valve 58 can also bc maintained in closed position, and sutllcient hydraulic lubricating fluid for replacing that removed from separator 28 and for lubricating pump 30 will be sucked from fluid body 40 in sump 26 along the outer lower surface of pipe 42 into the bottom thereof and along the inner surface of pipe 42 and through pump 30 and then forced through pipe 44 along with the mercury into the separator.

In operation of the above described embodiment, thc electronic signals actuating the control valve cause periodic shifting of the control valve such that when port 14 registers with intake port 5t) of the valve and port 24 registers with outlet port 32, the hydraulic mixture of the invention will circulate in conduits 18 and 20 in the direction shown by the arrows A, causing motor 12 to rotate in one direction, and when port 24 communicates with intake port 50 and port 14 registers with outlet port 32, the hydraulic mixture will' circulate in the opposite direction indicated by arrows A through these conduits, causing the motor to reverse its direction of rotation. However, it is seen that regardless of the position of: valve, 10, the: direction of flow' offluid in the remainder of.r thev system between outlet portv 32 and intake portSll is: always in the direction shown by arrows B.

If: it is desired. to increase the proportion of hydraulic lubricating fluid introduced into the mercury-containing mixture fed tointake port. 501 ofthe control valve so as to increase the. compression factorv ofthe hydraulic mixture circulating: between the control valve and motor, valve` 60' can be opened suflicientlyto permit introduction of the desired: greater amount of fluid 54 into pipe 52 in. proportion. to mercury from pool 56. Under these conditions valve 58 is also opened to permit introduction into pipe 42 of a correspondingly increased proportion of lubricating fluid 40 from sump 26. This enables a balanced. flow of fluid to be maintained between the sump and. separator. Reduction valve 48 controls the pressure maintained. inthe separator. Fluid from the separator passing this valve is returnedv via pipes 46 and 36 to the fluid body 40 in the sump.

It is seen according to the above embodiment of the invention that the hydraulic fluid mixture passing from the control valve to the motor and' return is composed of mercury with a variable amount of hydraulic lubricating fluid which in the most desired instances may be cut down to` only traces thereof, while in the remainder of the system the amount of hydraulic fluid generally predominates considerably over the quantity of mercury therein. Thus, where it is desired to confer on the hydraulic mixture between the control valve and motor a stiff spring action according to the invention principles, only a film of hydraulic lubricating fluid may be permitted to flow along the inner surfaces of conduits 18 and 20 with the mercury passing therethrough. Since the compression factor of a mixture of a hydraulic liquid of low compression factor such as mercury and conventional hydraulic fluids increases rapidly with the addition of comparatively small amounts of the latter, in the case of the invention mixtures containing mercury circulating between the control valve and motor, it is preferred not to employ more than about hydraulic lubricating fluid and most desirably not more than 1% thereof in such mixtures, on a volumetric basis. When using 1% of lubricating fluid in this connection, the compression factor of the mixture is in the neighborhood of about $5,200 at 1000 p. s. i., while the use of 10% of such fluid in these mercury-containing mixtures raises the compression factor to something in the neighborhood of 1/700 at 1000 p. s. i. However, even the latter represents a marked improvement over the 1/270 compression factor at1000 p. s. i. of conventional hydraulic fluids presently in use. v

Another feature of the invention is that only a comparatively small proportion of fluid of low compression factor as compared to hydraulic lubricating fluid is required in the overall system. This is particularly noteworthy as regards the preferredv use of mercury in the invention because of the high cost of this fluid. For example in the embodiment described above for use in the operation of a flight table, only 20 to 40 cu. in of mercury can be utilized with approximately 300 gallons of hydraulic lubricating fluid in the overall system. Moreover, in accordance with the invention principles as pointed out above, there is practically no loss of mercury a flight table and including a control valve actuated by mercury' according to the` invention', there isk a sharper response of the hydraulic motorv on actuation of the control valve, i. e. less lag between actuation of the control valve and corresponding response of the motor. The invention is particularly applicable, however, where the` hydraulic motor is controlled by a control valve actuated by radio signals and requiring almost instantaneous response of the motor in accordance with changes inthe control valve effected by such signals. The hydraulic system of the invention is eflicient, dependable, versatile and comparatively inexpensive.

Obviously many modifications andv variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

I claim:

1. In a hydraulic system, a hydraulic motor, valve means for controlling flow ofY hydraulic fluid to said motor, conduit means between said motor and valve means, a first mixture of immiscible hydraulic fluids circulating under pressure from said control Valve to said motor and back to said control valve, at least one of said fluids having a low compression factor and at least another of said fluids having lubricating properties, the amount of the former predominating over the amount of the latter on a volumetric basis, a second mixture disposed in another portion of said system, said mixture containing the same ingredients as said first mixture, said second mixture predominating on a volumetric basis in said fluid having lubricating properties, means for circulating exit fluid from said control valve to said second mixture, means for removing from said second mixture a third mixture of said fluid ingredients predominating in said fluid having a low compression factor on a volumetric basis, means for delivering said third mixture under pressure to the intake of said control valve, and means for selectively changing the proportion of said one and said another fluids in the mixture fed to said control valve.

2. In a hydraulic system as defined in claim 1, wherein each ofV said mixtures consistsof two immiscible hydraulic fluids, one of said fluids being mercury, the other having lubricating properties.

3. In a hydraulic system as defined in claim 2, Wherein said first mixture contains up to 15% of said fluid having lubricating properties on a volumetric basis.

4. In a hydraulic system as defined in claim 1, including means for selectively changing the proportion of said one and said another fluids in the mixture removed from said second mixture.

y 5. In a hydraulic system, a hydraulic motor, a control valve for said motor, a first conduit connecting the exit port of said control valve with the intake port of said motor, a second conduit connecting the exit port of said motor with a return port in said control valve, a first mixture of immiscible hydraulic fluids circulating under pressure in said conduits, at least one of said fluids having a low compression factor and being denser than any other fluid in said mixture, and at least another of said fluids having lubricating properties, a container for collecting fluid, a third conduit connecting the return port of said control valve with said container for conveying said mixture thereto, said container having a second mixture therein containing the same ingredients as said first mixture and predominating on a volumetric basis in said fluid having lubricating properties, the other denser fluid being located at the bottom of said container, a rereceptacle, a fourth conduit connected to said receptacle and communicating with the body of said denser fluid at the bottom of said container, a pump in said fourth conduit for raising the pressure of fluid transferred from said container to said receptacle, means for introducing a minor volumetric proportion of hydraulic fluid having lubricating properties from said container into said fourth conduit along with said denser fluid, a fifth conduit connecting the lower portion of said receptacle with an intake port in said control valve, said receptacle containing a third mixture of said iiuid ingredients predominating in said fluid having lubricating properties on a volumetric basis, and means for injecting fluid having lubricating properties from said receptacle into the denser fluid flowing from the bottom of said receptacle into said fth conduit to forni the mixture circulating between said control valve and motor.

6. In a hydraulic system as defined in claim 5, wherein the first uid mixture circulating between said control valve and motor contains a maor proportion of said fluid having a low compression factor and a minor proportion of fluid having lubricating properties, on a volumetric basis.

7. In a hydraulic system, a hydraulic motor, a control valve for said motor, a first conduit connecting the exit port of said control valve with the intake port of said motor, a second conduit connecting the exit port of said motor with a return port in said control valve, a first Vmixture of immiscible hydraulic fluids circulating under pressure in said conduits, said mixture consisting of a major proportion of mercury and a minor proportion of a less dense hydraulic fluid having lubricating properties on a volumetric basis, a container for collecting fluid, a third conduit connecting the return port of said control valve with said container for conveying said mixture thereto, said container containing a second mixture of said fluids with a substantially larger proportion of lubricating uid volumetrically than said first mixture, a receptacle, a fourth conduit connected to said receptacle and communicating with the mercury at the bottom of said container, a pump in said fourth conduit for increasing the pressure of fluid transferred from said container to said receptacle, means for injecting a minor proportion of hydraulic lubricating fiuid disposed in said container above said body of mercury into said fourth conduit along with mercury, a fifth conduit connecting the lower portion of said receptacle with an intake port in said control valve, a third mixture of mercury and said hydraulic iiuid having lubricating properties in said receptacle under pressure, means for injecting hydraulic lubricating fiuid disposed in said receptacle over the body of mercury therein into the mercury E "ng from said receptacle into said fth conduit to f z the mi. e circulating between said control valve References Cited inthe le of this patent UNTED STATES PATENTS 433,1 4 Pickles July 29, 189() 732,908 Thomson July 7, 1903 1,912,314L Simpson May 30, 1933 

